As a heat exchanging device for drying, heating or cooling a variety of powder, an indirect heat transfer agitating type dryer is known.
The one disclosed in, for example, Japanese Examined Patent Application Publication No. S48-44432 (Patent Literature 1, hereinafter) is known as such an indirect heat transfer agitating type dryer. The disclosed device is so configured that a shaft is rotatably supported within a horizontally long casing, that a plurality of heat exchangers are disposed at predetermined intervals on the shaft, and that a heat exchanging medium is supplied into the heat exchangers via the shaft. In this device the powder is dried (heated, cooled) by indirect heat transfer from the shaft and heat exchangers.
Here, the heat exchanger disclosed in Patent Literature 1 uses a wedge-shaped hollow rotating body 50, as shown in FIG. 14. This wedge-shaped hollow rotating body 50 is formed by bringing two pieces of fan-shaped plate materials 51, 51 into contact with each other at one side of their ends while separating the plate materials 51, 51 at the other side to block the periphery thereof with plate materials 52, 53. Therefore, the hollow rotating body 50 is shaped into a wedge in which a front end part 54 at the leading end in a rotation direction forms a line, while a rear end part 55 at the rear end in the rotation direction forms a surface. Two of the wedge-shaped hollow rotating bodies 50 are then disposed as a pair with certain gaps A, A therebetween so as to be symmetric with each other with respect to a shaft 60, as shown in FIG. 15. The two wedge-shaped hollow rotating bodies 50 form a pair and a plurality of the pairs are disposed at predetermined intervals in an axial direction of the shaft 60.
The disclosed in Patent Literature 1 had the following excellent characteristics:
(1) Small installation area and size.
(2) Large heat transfer coefficient and high heat efficiency.
(3) Self-cleaning effect achieved by the wedge-shaped hollow rotating bodies.
(4) The temperature of an object to be processed and the time for processing it can be controlled easily.
(5) Powder with high moisture content can be processed.
(6) Excellent piston flowability (transferability) of the object to be processed.
However, the device described in Patent Literature 1 has such a problem that when the object to be processed is brittle and fragile, it receives a compression force from the wedge-shaped hollow rotating bodies 50 serving as the heat exchangers and thereby becomes pulverized.
Also, a problem in producing the shaft provided with the wedge-shaped hollow rotating bodies is that it requires an enormous amount of time due to the shape of the shaft with the rotating bodies. In other words, the wedge-shaped hollow rotating body 50 is created by disposing the two pieces of fan-shaped plate materials 51, 51, isosceles triangular plate material 52, and trapezoidal plate material 53 in the manner shown in FIG. 16 and welding the entire periphery of the abutting parts. Therefore, when forming a single heat exchanger, the welding process comprises a plurality of processes, and automation of the welding operation is difficult. Furthermore, it is difficult to fix the obtained heat exchanger to the shaft 60. This is because, in order to secure the heat exchangers to the shaft 60, first a plate material 61 formed with notches which are substantially the same shape as a part (opening part) of each heat exchanger that is in contact with the shaft 60, is lined (welded) on the entire outer peripheral surface of the shaft 60, and thereafter the plate material 61, the shaft 60 and the parts of the heat exchangers abutting on the plate material 61 and the shaft 60 need to be welded at the entire periphery of the abutting sections. In such welding, the welding methods of each layer need to be changed. For this reason, the problem of the device described in Patent Literature 1 is that an enormous amount of time is required in forming the heat exchangers.
There is also a device in which a plurality of hollow disks are simply attached to a shaft as heat exchangers. Such a hollow disk-shaped heat exchanger, however, cannot ensure the piston flowability of the object to be processed, which is an excellent characteristic of the wedge-shaped hollow rotating body disclosed in Patent Literature 1. The reason is because, as shown in FIG. 15, the piston flowability of the object to be processed can be secured for the first time by allowing the object to be processed to pass regularly through the gaps A, A of the two wedge-shaped hollow rotating bodies 50, 50 attached to the shaft 60.
Here, the piston flowability are important factors for realizing the first-in-first-out phenomenon of the object to be processed and obtaining residence time, heat history, and reaction time to keep each particle of the powder even, and are important attributes of the heat exchanging device in order to maintain the consistent quality of the object to be processed.
The gaps A, A described in Patent Literature 1 function to transfer powder layer formed at the nearest part (upstream side) within the device from a raw material feeding port side to a product discharge side. At this moment, the wedge-shaped hollow rotating body 50 itself does not have an extrusion force that a screw has. For this reason, in this device, the powder is sliced regularly, such as twice per rotation, in order to be transferred by the gaps A, A simply using the pressure of the powder. Therefore, back mixing or short pass seldom occurs on the powder in this device, so that “the first-in-first-out phenomenon” can be ensured and the piston flowability can be realized. On the other hand, in the case of the device in which simple hollow disk-shaped heat exchangers are attached to the shaft, the object to be processed is transferred from a gap between a casing and each heat exchanger to a downstream side. As a result, the back mixing or short pass phenomenon occurs where a part of the powder layer in the vicinity of the shaft remains in its position, while a part of the same near the casing moves rapidly, whereby the piston flowability cannot be realized.
The present invention has been contrived in view of the above problems of the background art. An object of the present invention is to provide a heat exchanging device for powder, which is capable of suppressing the compression force applied to an object to be processed, as much as possible, while ensuring the piston flowability of the object to be processed, and reducing the manufacturing man-hour (time), as well as a method for manufacturing the heat exchanging device.